A major limiting factor in biochemical studies of carcinogenesis is methodology. No methods are available for investigating directly cause and effect relationships between an initially observed chemical lesion in some macromolecule and development of a tumor. The immediate goal of this research is to develop a direct method for introducing a potentially carcinogenic, chemical change at a single, known, preselected position in a DNA molecule. By studying the biological effects of this change, it should be possible to establish whether or not this particular change can lead to malignancy. Our approach is based on the total synthesis of DNA by a combination of chemical and biochemical techniques. A series of synthetic DNA's carrying site-specific modifications corresponding to changes known to be produced by different chemical carcinogens will be synthesized and tested for mutagenicity and carcinogenicity by transformation of suitable cell lines. This research has three long-range goals: (1) to determine which of the site-specific modifications that known carcinogens produce in DNA leads to mutations; (2) to determine the type of mutation produced by different premutational lesions in DNA; (3) to determine whether or not any of these premutational lesions cause transformation of normal cells into malignant cells.